My new adventure with my Microbee Premium Series

[The_Huck]

I noted only 9V on pins 1 & 2 on connector X5 and the schematic indicates it should be 12V.
When I measure the output of the power supply unloaded, I get 11.5V. When I plug the computer in, it drops to 9V again.

When powering from my bench supply set to 12V, I get 11.5V on pins 1 & 2 and at the input to the voltage regulators, and 5V on the regulator output. The computer is consuming around 920mA.

With the core board installed, I checked the composite with the scope and I'm getting a constant 1.66V at the output.

The reset is still showing as low.

Note: I'm using schematic 8501-3-01 whereas my board is 8501-03-04CR so connector X4 on the schematic translates to connector X5 on my board. It appears there may not be a schematic for my revision of board.

Now I need to figure out what's holding the reset low.

---

After plugging in the power and video, along with the drive cable I fired up the Bee.
No signs of life unfortunately.

I'll start by measuring voltages and going from there. I can't see a power LED on the computer unit so I'm not sure if power is actually getting to it.

I'm assuming the video output is standard composite?

When I power up the drive unit by itself, I can hear a drive spin up.
If I power the drive unit with everything connected, I see the access LED light on the left drive.
I put in the boot disk and power cycled but I did not hear any boot type action from the drive. It sounds like the drive did seek though.
The drives are in unknown condition so I will also confirm they work on a PC. I assume they are PC style drives?

There is no power LED on the computer.
Seeing that you have a light on 'A' drive when it is all plugged in means that you have power o.k. to the drives and the computer.
If there was some problem with power in the keyboard, neither of the drive LEDs would show (just like if you disconnect the 34 way drive cable).

The video output is composite - correct. The easiest way to get a video output is to use the AV input of a TV, and although this might have sync issues with a not so steady display, at least you will know if 
you have something on the screen.  With the computer not booting from disk, if the display is working correctly, you should see a block cursor at the top left of the screen, and nothing else.
If you get nothing on the screen at all, then there is something wrong with the computer and the first thing to do there is open the case and remove the top board from the 2 x  25 way pin strip sockets
that connect the top board to the main board - unplug & plug back in multiple times.  If the unit has been sitting for some time, it may have poor oxidized connections on these pins. Unplugging and plugging
the board in again a few times can get over this problem.
I wouldn't worry about testing the drives until you get something on the screen.  Most likely the drives are o.k. and when the computer is working properly, it will boot from the drives o.k. as well.

There is also the option of sending your machine to us for repair, but I understand that fixing retro stuff yourself is part of the hobby.

That could be an option.
I have limited knowledge in this area but I'm keen to learn some of these troubleshooting techniques.
I'm going to apply what I learn here to help fix up a dead Dick Smith Wizzard and a couple of IBM PC boards.